Fatty acid amides (FAAs) represent a novel family of endogenous signaling lipids implicated in a broad range of neurophysiological processes, including pain, sleep, feeding, and memory. A prototype FAA anandamide may serve as an endogenous ligand for the central cannabinoid (CB1) receptor. Although anandamide binds and activates the CB1 receptor in vitro, this compound induces only weak cannabinoid behavioral effects in vivo, possibly as a result of its rapid catabolism. Currently, our understanding of the mechanisms by which anandamide and related FAAs are produced and catabolized in vivo remains limited. The objective of this proposal is to identify and characterize enzymes that regulate the levels and activities of FAAs in vivo. One candidate enzyme responsible for terminating FAA signals in vivo is fatty acid amide hydrolase (FAAH), which hydrolyzes anandamide and related FAAs in vitro. To test the role that FAAH plays in regulating FAA function in vivo, we have created a mouse model in which this enzyme has been genetically deleted (FAAH-/- mice). FAAH-/- mice are severely impaired in their ability to degrade FAAs and exhibit an array of intense CB1 -dependent behavioral responses to anandamide, including hypomotility, analgesia, catalepsy, and hypothermia. FAAH-/- mice possess greatly increased endogenous brain levels of anandamide (and several other FAAs) and display reduced pain sensation that is reversed by the CB1 antagonist SR141716A. These data indicate that FAAH is a key regulator of FAA signaling in vivo, setting an endocannabinoid tone that modulates pain perception. In this application, we propose to extend our pharmacological and behavioral analysis of FAAH +/+,+/-, and -/- about, and -/- mice to examine the role that anandamide and related FAAs play in regulating multiple forms of acute and chronic pain sensation. We will also use these animal models to elucidate interactions between the endogenous cannabinoid and opioid systems. Finally, we plan to isolate and molecularly characterize enzymes that biosynthesis FAAs. These studies will elucidate key enzymes that regulate FAA signaling in vivo, and these proteins may represent new targets for the treatment of pain, addiction, and other neurological disorders.